Glucose-stimulated insulin secretion is driven by the coordinated Ca2+ response in pancreatic islets following glucose elevation. In mouse islets, spatial and temporal Ca2+ dynamics are disproportionally controlled by subpopulations of β-cells, as identified by optogenetics. It is unknown which factors underlie this functional heterogeneity of β-cells in intact islets. Here, we tested if distinct β-cell subpopulations may be identified based on Ca2+ response to glucose elevation, and if their Ca2+ uptake efficiency, metabolic activity and electrical coupling are significantly different. We used MIP-CreER GCaMP6s mouse model which expresses Ca2+-sensitive GFP specifically in β-cells. We performed simultaneous Ca2+ dynamics and metabolic activity (NADH) response to [2-11] mM glucose elevation, along with gap junction permeability measurements in individual islets. We observed three functional subpopulations of β-cells distinct from an islet average: cells with 1) the fastest response to glucose elevation (1st responders); 2) the fastest 2nd phase oscillatory Ca2+ response (wave-initiators); and 3) the non-coordinated Ca2+ oscillations (un-coordinated). While 1st responders and wave-initiators were in different sub-regions of the islet, both subpopulations accumulated more Ca2+ during initial Ca2+ elevation (p=0.0403, p=0.0101) compared to the islet-average. Wave-initiators were more metabolically active (p=0.0223). The un-coordinated cells accumulated less Ca2+ (p<0.001) and were less metabolically active (p=0.0296). Gap junction permeability was not significantly different between subpopulations.
In conclusion, the 1st phase Ca2+ uptake and 2nd phase Ca2+ oscillations emerge in spatially- and metabolically-distinct subregions of the islet. This is likely due to increased metabolic activity of the β-cells in these regions which leads to greater membrane depolarization and thus, disproportionately enhances the islet Ca2+response. (NIH R01 DK102950 R01 DK106412)
V. Kravets: None. R.A. Piscopio: None. W. Schleicher: None. R.K. Benninger: None.
National Institutes of Health